A stent is a generally tubular medical device which, for treatment of various diseases arising from stenosis or occlusion of a blood vessel or other living body lumen, is indwelled in the stenosed or occluded part to dilate the part and secure the lumen (i.e., keep the lumen in an open state).
The following describes an example in which the stent is used in a blood vessel. The stent is a body which, for insertion from the outside into the inside of a living body, is small in diameter at the time of insertion, and is expanded at the target stenosed or occluded part so as to be enlarged in diameter and to maintain the lumen as it is (i.e., in an open state).
In general, stents are hollow cylindrical bodies obtained by processing metallic wires or a metallic pipe. A stent is mounted to a catheter or the like in a radially reduced state, is inserted into a living body, and is expanded in a target part by some method, to be fixed in close contact with the inner wall of the lumen at the target part, thereby maintaining the lumen in an open state. The stents are classified by function and placement method into self-expandable stents and balloon-expandable stents. A balloon-expandable stent is a stent which itself does not have an expanding function. The balloon-expandable stent is used in a method in which the stent mounted on a balloon is inserted into a target part, and thereafter the balloon is dilated to expand (plastically deform) the stent by the dilation force of the balloon, thereby fixing the stent in close contact with the inner surface of the target lumen. This type of stent requires the stent-expanding operation as described above. On the other hand, a self-expanding stent is a stent which itself is provided with an expanding function. The self-expanding stent is used in a method in which the stent contained in a radially contracted state within a stent-containing tube body is inserted into a living body, and is discharged from the stent-containing tube body at a target part so as to automatically return into its original expanded state, thereby being fixed in close contact with the inner wall of the lumen at the target part and maintaining the lumen shape in an open state.
The purpose of the placement of a stent at present is to return a blood vessel stenosed for some reason to its original open state. In most cases, the stents are mainly for preventing or reducing the risk or extent of restenosis which might occur after such a procedure as PTCA. In recent years, to suppress the probability of restenosis more assuredly, drug-eluting stents with a drug such as immunosuppressor or carcinostatic loaded on the stent are also used, and the effect is generally known.
Most of the self-expanding stents are used in peripheral regions such as blood vessels of inferior limb and carotid arteries. An example is disclosed in International Application Publication No. WO 96/26689 (JP-T-H11-505441.
In this known system, the self-expandable stent is contained in a stent-containing tube body in a stent delivery system. Due to the self-expanding property of the stent, the positioning of the stent at the time of placement is difficult as compared with the case of a balloon-expandable stent. In addition, a jumping phenomenon may occur in which the stent jumps out of the stent-containing tube body unguardedly. If this phenomenon occurs, the stent would be disposed at a position deviated from the planned position. It may in some cases be necessary to readjust the placement position after the stent is exposed to a certain extent from the stent-containing tube body during the stent placement procedure. In the case of the known system, however, it is difficult to re-contain the stent into the stent-containing tube body (i.e., to once again load the stent in the stent-containing tube body).